Re: [libvirt] [PATCH 4/6] qemu: Wire up disk model=virtio-{non-}transitional

On Sun, Jan 13, 2019 at 06:12:06PM -0500, Cole Robinson wrote: > Add new <disk> model values for virtio transitional devices. When > combined with bus='virtio': > > * "virtio-transitional" maps to qemu "virtio-blk-pci-transitional" > * "virtio-non-transitional" maps to qemu "virtio-blk-pci-non-transitional" > > Signed-off-by: Cole Robinson <crobinso(a)redhat.com&gt; > --- > src/qemu/qemu_command.c | 31 ++++++++++++++++++- > src/qemu/qemu_domain_address.c | 2 ++ > ...virtio-non-transitional.x86_64-latest.args | 7 +++-- > .../virtio-transitional.x86_64-latest.args | 4 +-- > .../virtio-non-transitional.xml | 10 ++++-- > 5 files changed, 45 insertions(+), 9 deletions(-) > > diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c > index 822d5f8669..ca6abea227 100644 > --- a/src/qemu/qemu_command.c > +++ b/src/qemu/qemu_command.c > @@ -443,6 +443,33 @@ qemuBuildVirtioDevStr(virBufferPtr buf, > return 0; > } > > +static int > +qemuBuildVirtioTransitional(virBufferPtr buf, > + const char *baseName, > + virDomainDeviceAddressType type, > + bool transitional, > + bool nontransitional) > +{ > + if (qemuBuildVirtioDevStr(buf, baseName, type) < 0) > + return -1; > + > + if (type != VIR_DOMAIN_DEVICE_ADDRESS_TYPE_PCI && > + (transitional || nontransitional)) { > + virReportError(VIR_ERR_CONFIG_UNSUPPORTED, > + _("virtio transitional models are not supported " > + "for address type=%s"), > + virDomainDeviceAddressTypeToString(type)); > + return -1; > + } > + > + if (transitional) { > + virBufferAddLit(buf, "-transitional"); > + } else if (nontransitional) { > + virBufferAddLit(buf, "-non-transitional"); > + } > + return 0; So this only works on QEMU >= 4.0.0 - earlier versions will fail to start. We can, however, make it work correctly with old QEMU. A transitional device is 100% identical to the existing device types, so we can simply not add the "-transitional" suffix for old QEMU. The only difference is the way libvirt does PCI bus placement of the transitional device - we'd never use PCIe. A non-transitional device is identical to the existing device types, but with disable-legacy=true set.

QEMU guarantees this compatibility of the different devices, but only for machine types < pc-i440fx-4.0.0 / pc-q35-4.0.0. So we should none the less make sure we use the modern device names for any QEMU which genuinely supports them.